The present invention relates to a structure of a sensor designed to get a CMOS image sensor acting in a wide dynamic range of light intensity and a method of obtaining image signals according to the structure.
A CMOS image sensor is a type of sensor made by using the manufacturing technology of CMOS, which converts the incident light onto each pixel of the sensor to electrons by using photodiode, and outputs a voltage signal in proportion to the number of electrons thereby forming an image.
The dynamic range of a conventional CMOS image sensor, in which the sensor properly responds to light intensity is about 60 dB. That is to say, it can normally output a signal ranging from the least sensible intensity of light to about 1,000 times brighter light. Various attempts have been made to expand the dynamic range of a CMOS image sensor.
For example, U.S. Pat. No. 7,443,427 discloses a pixel structure with a logarithmic response, and U.S. Pat. Nos. 7,442,910 and 7,209,166 disclose methods for increasing the dynamic range by changing a storage capacitor for electrons within a pixel, via manipulation of switches.
Further, Korean Patent Nos. 0835894 and 0865111, and U.S. Pat. No. 7,489,352 disclose methods employing two sized photodiodes by which two signals with different light responsivity are outputted therefrom.
There are also other methods to increase the dynamic range of a sensor by repeatedly operating a transfer gate or reset transistor during the process of obtaining signals in a widely used pixel with a 4-transistor structure.
The above various solutions used for the expansion of the dynamic range have their own merits together with demerits, and thus it is difficult to say which one has the remarkable technical advantages.